1. Field of the Invention
The present invention relates to a process for the preparation of a color liquid crystal display device suitable for use in color televisions, personal computers and the like, and a color liquid crystal display device produced thereby.
2. Related Background Art
With the advancement of personal computers, particularly, portable personal computers in recent years, the demand for liquid crystal display devices, particularly, color liquid crystal display devices tends to increase. It is however necessary to reduce the cost of the color liquid crystal display devices for further spreading them. There is an increasing demand for reduction in the cost of color filters particularly given much weight from the viewpoint of the cost.
Various processes have heretofore been attempted for meeting the above demand while satisfying properties required of the color filters. However, no process satisfying all the required properties is yet established under the circumstances. The typical processes for the preparation of color filters will hereinafter be described.
The first method is a pigment dispersing process. In this process, a layer of a photosensitive resin, in which a pigment has been dispersed, is first formed on a base and then subjected to patterning, thereby obtaining a pattern of a single color. This step is repeatedly performed three times, thereby forming a color filter composed of colored patterns of R (red), G (green) and B (blue).
The second method is a dyeing process. In the dyeing process, a water-soluble polymeric material, which is a material to be dyed, is applied to a base, and the coating film thus formed is patterned in the desired form by a photolithographic process. Thereafter, the base on which the coating film has been patterned is immersed in a dye bath to obtain a colored pattern. This step is repeatedly performed three times to form a color filter composed of colored patterns of R, G and B.
As the third method, there is an electrodepostion process. In this process, a transparent electrode is first patterned on a base. The base is then immersed in an electrodeposition coating fluid containing a pigment, a resin, an electrolytic solution and the like to electrically deposit the first color. This step is repeatedly performed three times, thereby forming a color filter layer composed of colored patterns of R, G and B. Finally, this color filter layer is calcined to form a color filter.
The fourth method is a process in which pigments are separately dispersed in a thermosetting resin, the resultant thermosetting resin dispersions of R, G and B colors are separately applied to a base by repeating printing three times, and the resin portions thus applied are then thermoset to form a layer composed of colored patterns of R, G and B, thereby forming a color filter.
It is general to form a protective film on the colored layer in each process.
The need of repeating the same step three times to form the colored patterns of R, G and B is common to these processes. Therefore, the production cost is necessarily increased. There is also offered a problem that a yield is reduced as the number of steps increases. Besides, in the electrodeposition process, formable patterns are limited. It is hence difficult to apply this process to a TFT color liquid crystal display device in the existing technique. Further, the printing process involves a drawback that resolution is poor, and is hence unfit to form fine-pitch patterns.
In order to eliminate these drawbacks, processes for producing a color filter by using an ink-jet system have been proposed in Japanese Patent Application Laid-Open Nos. 59-75205, 62-109002, 63-235901, 1-217302, etc.
In particular, the following problems arise upon the production of a color filter according to the ink-jet system.
(1) Color mixing at boundaries between adjacent pixels of different colors; and
(2) Blank areas occurred at boundaries between colored portions and black matrices, and color irregularity caused by the distribution of optical density in colored pixels.
A method for preventing the color mixing at boundaries between adjacent pixels in a color filter has been proposed in Japanese Patent Application Laid-Open No. 8-75916. According to this method, ink-phobic portions are formed by exposure using a photomask, thereby bringing about an effect of preventing the color mixing between inks. However, this process requires to newly produce a mask for exposure when a cell size is changed due to a change in the size or resolution of a liquid crystal display device, or the like. The exposure step in this process is required to align with black matrices with high precision, and so the process is disadvantageous from the viewpoints of yield and cost.
Therefore, a method to conduct back side exposure using black matrices in place of a mask has been proposed (refer to Japanese Patent Application Laid-Open No. 8-227012).
On the other hand, black matrices are subject to such wide variations as their material is Cr or a resin, and they are provided on a substrate opposite to a color filter substrate or on a TFT substrate. Accordingly, the process for the preparation of a color filter must be changed according to the type of black matrices.